This invention relates to the field of linear broadband signal generation, processing, and capture/analysis. Typical broadband signal generation devices include, but are not limited to, arbitrary waveform generators, digital pattern generators, and RF signal generators. Typical broadband signal processing devices include, but are not limited to, amplifiers and attenuators. Typical broadband signal capture/analysis devices include, but are not limited to, oscilloscopes, waveform recorders, spectrum analyzers, and bit error rate testers. Network analyzers are another common class of broadband device that performs both signal generation and analysis. The term “broadband” as used herein refers to systems that cover a contiguous band of frequencies starting at zero Hertz (Hz) (or low frequencies near 0 Hz) and extending well into the radio frequency (RF) and/or microwave range, which includes signal frequencies of at least 100 MHz and higher. A system with frequency coverage extending to zero frequency is commonly referred to as being “DC-coupled.”
The signals in these broadband systems may exist in either digital or analog form, or a combination thereof. The systems may include analog to digital converters (ADCs) and/or digital to analog converters (DACs), which are collectively referred to as “data converters”.
It is often necessary to do linear processing of signals while they are in analog form. However, linear signal processing components such as amplifiers, attenuators, DC level shifters, and balanced-to-unbalanced converters (commonly known as “baluns”) are not amenable to working over a very large bandwidth, especially when the bandwidth extends to low frequencies near or at 0 Hz. These limitations are well known to persons skilled in the art of analog circuit design. For example, amplifiers that can handle zero Hertz have inferior performance compared to more narrowband amplifiers in terms of noise, distortion, and efficiency. There remains a need for an improved broadband system for linear signal processing.